mid year big block running hot

[Anthony S.]

What is the root cause of the big block cars overheating issues? Right now I am trying to help a friend solve this issue.
Concern is that it is an engine design problem (from day one), rather than other causes (engine timing, bad H2O pump, radiator cap not holding pressure....etc.)
Any advice/insight appriciated Thanks Tony

[Joe L.]

Re: mid year big block running hot

What is the root cause of the big block cars overheating issues? Right now I am trying to help a friend solve this issue.
Concern is that it is an engine design problem (from day one), rather than other causes (engine timing, bad H2O pump, radiator cap not holding pressure....etc.)
Any advice/insight appriciated Thanks Tony

Tony------

It's not engine design although, certainly, big blocks have more heat rejection to accommodate than small blocks. However, all Corvette big blocks were always fitted with high capacity radiators.

For C2's I believe a big part of the problem relates to inefficient radiator shroud design and, most importantly, the lack of effective sealing between the radiator and the shroud. Adding to this is rather limited air intake (grille) surface area.

[Wayne W.]

Re: mid year big block running hot

The most common problem with BB heating that I have encountered in my 40+ years of driving and working on them is, the radiator core. Over time the solder joints from the tubes to the fins crack and it loses cooling capacity. Re-coring or a new radiator usually solves the problem. Now, that assumes the radiator shroud and the fan clutch is correct and in good condition.

[William C.]

Re: mid year big block running hot

Need much more info, how hot? what conditions. new parts, old parts? What parts and condition for all the components of the system Engine, rad, fan, FAN CLUTCH. What analysis has been done, what conditions, temp, engine load, They (BB) all run hot, but the system is designed to handle hot, is it dumping coolant? High gauge reading? If not dumping coolant, have you verified the gauge is accurate?

[Duke W.]

Re: mid year big block running hot

What Bill said, and normal operating temperture is up to 230F in hot weather low speed driving.

All L72 and L71 big blocks have ported vacuum advance, and after after 1967 all big block have ported vacuum advance. Changing to full time can considerably ameliorate low speed overheating, but some will require a different spec VAC.

What model year/engine configuration are we dealing with. Has it been modified? How so?

It's not uncommon on a 40+ year old car that the engine and cooling system have been turned into a total kluge by backyard engineering, so you need to provide much more specific information on the operating conditions and engine/coolling system configuration.

Duke

[Michael J.]

Re: mid year big block running hot

I would agree with these comments, after having solved mine through several lines of upgrades. I will also show you, as a Shelby guy too, a reason the late '60s 428 Cobra Jet FE engines did not have this problem, a uniquely designed valve to switch from ported to full time vacuum advance when engine temps trigger it:

http://www.428cobrajet.org/id-dist-vac-valve

[Clem Z.]

Re: mid year big block running hot

if you want to try a quickie just put a restrictor in the hose that runs from the water pump to the intake manifold. use a cup type brass expansion plug with a 1/8" dia hole forced into the hose and see what happens. when racing BBC we had heating problems till we eliminated this hose as too much water bypasses the rad and goes from the intake directly into the water pump bypassing the rad. when everything is new this may not be a problem but as the rad looses efficiency you could have a problem. also make sure the foam rubber seal that seals to the hood and top of core support is there

[Tom N.]

Re: mid year big block running hot

I have run my '67 big block in Arizona ...YES, with A/C in 112* and never over heated.
I have an aftermarket 4 core aluminum radiator with a new GM fan clutch and the Edelbrock
hi-pro water pump...hope this helps.

[Anthony S.]

Re: mid year big block running hot

Two cars having this issue


1) one at higher speeds , going 65 -75ish, 355 rear, stock engine but timing advanced
Stock engine. Rad may be tired. Fan clutch recent rebuild five years ago. Temp gets to about 190 to 195, sometimes near 200 in hot weather. Fan clutch adjustment advice would be helpful.

2) second car get s hot in stop and go traffIc, up to near 210. Engine rebuild all to original specs .
New Al rad & using a fan in front of rad.
Thanks. T

[Wayne W.]

Re: mid year big block running hot

Doesn't sound like too much of a heating problem.

[William C.]

Re: mid year big block running hot

Reading about within the tolerance of the sending unit about what my last bigblock ran...

[Michael J.]

Re: mid year big block running hot

My BB L71 runs about 210-220 in warm weather stop and go, nothing unusual and it won't hurt it.

[Duke W.]

Re: mid year big block running hot

IIRC you converted your L71 from ported to full time vacuum advance. To take full advantage of this on L71 a B20 or B26 VAC should be installed and the intial timing bumped to the 8-12 degrees range.

Duke

[Duke W.]

Re: mid year big block running hot

I would agree with these comments, after having solved mine through several lines of upgrades. I will also show you, as a Shelby guy too, a reason the late '60s 428 Cobra Jet FE engines did not have this problem, a uniquely designed valve to switch from ported to full time vacuum advance when engine temps trigger it:
http://www.428cobrajet.org/id-dist-vac-valve

I'm pretty sure GM used a similar system beginning sometime in the early to mid-seventies, but I'm not sure what it was called. It may have been part of what was called CCS - Combustion Control System.

It's tough to keep track of all the various emission control systems and devices and came and sometimes went during that era. It was also a very difficult time for the engineers to meet emission standards along with CAFE bogeys and keep the engines from overheating in worst case conditions.

Fortunately the three way catalyst and O2 sensor came along in the late seventies to save everybody from those terrible seventies engines, which had very crude emission control technologies that led to a lot of consequential issues.

Duke

[Robert K.]

Re: mid year big block running hot

Changing to full time can considerably ameliorate low speed overheating
Duke

Dang, Duke

I had to consult Webster to figure out whether or not it was helping.